1. Field of the Invention
The present invention relates to a magnetic disk drive system which can be connected to a computer for writing or reading data, more particularly relates to a magnetic disk drive system which can correct manufacturing error in a distance between a write head and a read head (hereinafter referred to as the xe2x80x9cwrite/read head distancexe2x80x9d) and thereby adjust a timing of writing data to the magnetic disk and raise a format efficiency of the disk and which can adjust a head position when reading data from the magnetic disk and thereby raise a track density.
2. Description of the Related Art
A magnetic disk drive system is essential in computer data processing. The spread of PCs has led to use of hard disk drives (HDD) for recording and for reading and reproducing data. Recently, hard disk drives have found uses beyond PCs and have been increasingly used in for example audio-visual systems, car-mounted systems, etc. Further, the information handled there has also become more diverse and the amount of the data handled has become enormous in many cases. The recording capacity of magnetic drive systems is therefore being increased.
In order to meet the demand for increased capacity in recent magnetic disk drive systems, magnetoresistive (MR) head units designed to handle high bit densities are often used for the magnetic heads. A magnetoresistive head unit has a read head and write head in a single unit. A magnetoresistive element is generally used for the read head, while an inductive element is used for the write head. The read head and the write head are separated by exactly a specific distance between their core centers when seen along the track direction. Further, the core centers are arranged offset by exactly a specific distance in the radial direction of the magnetic disk. Further, the head unit itself is attached to a head arm with a specific angle. Therefore, when the head unit moves over the magnetic disk, the head unit and head arm change in positional relationship with the tracks on the magnetic disk. Accordingly, the on-track timing differs between the read head and write head depending on the track position of the magnetic disk.
Summarizing the problems in the related art, as stated above, such a magnetic disk drive system is often used as a data storage device of a computer etc. Further, a magnetoresistive head unit is often used for the magnetic head of this magnetic disk drive system. This magnetoresistive head unit realizes high bit density recording by being provided with a separate read head core and write head core in a single unit.
The read head core and write head core used in this magnetoresistive head unit, however, are delicate elements. Further, when being assembled into a magnetic head unit, since the read head core and the write head core are separately arranged, manufacturing differences occur in the relative position of the read head core and the write head core among different units.
Further, in general, a magnetic disk device uses a rotation mechanism along with a magnetic disk and head carriage. Therefore, depending on the position of the magnetic head unit, the angle between the axial line of the magnetic head unit and a track changes and the distances with respect to a track from a center of the read head core and a center of the write head core in the track direction change. Further, since the distance between the write head core and read head core varies for each magnetic head unit, the position where positioning information to be read by the read head core is written on the magnetic disk ends up changing depending on the magnetic head unit.
In the related art, a fixed distance has been given not considering the difference in the magnetic head unit from the design target distance or the average distance at the time of manufacture and the timings at a write operation and read operation changed by that amount. The margin with respect to the difference has resulted in extra time in the format.
When writing positioning information to be read by the read head core at a certain timing, when actually written on the magnetic disk, deviation occurs in the written position according to the magnetic head unit due to the difference in the distance between the write head core and the read head core.
If the deviation in the write position becomes large, the phenomenon of the positioning servo information being written over and erased occurs. To prevent such a write-over phenomenon from occurring, it is necessary to give a sufficient margin of time to the format. When employing this measure, the format efficiency ends up deteriorating by the amount of that margin of time. Further, the recent rise in transfer rates and the higher bit densities in systems using magnetic disks have made systems more susceptible to the effects of error in the distance between the write head core and read head core. The deterioration in the format efficiency can no longer be ignored.
Further, since the read head core and the write head core are separate in this magnetic head unit, differences in manufacture result in a deviation at the center of the read head core and the center of the write head core. Since a rotation mechanism is used together with the magnetic disk and head carriage, the angle between the axial line of the magnetic head unit and a track changes depending on the position of the magnetic head unit and the amounts of deviation of the center of the read head core and the write head core from the track changes. Due to this phenomenon, in the past, the track position has been changed to measure the off-track margin and the correction positions connected by a line for use in correcting the amounts of deviation of the cores.
Even if taking such a measure, however, in recent years the track density of the systems used has been made higher and therefore linear correction is no longer sufficient for correction. Therefore, the problem arises of the trouble of not only the error rate rising, but also the data recorded on the adjoining track being erased. Further, if trying to reduce the error by linear correction, it is necessary to increase the measurement points. This being so, a tremendous amount of time has to be spent for measuring the offset margin at the time of shipment corresponding to the increase in measurement points. This makes this technique unsuitable for mass production. Further, due to the increase in the measurement points, there are the problems that the correction values also become more numerous, the amount of tables for storing the correction values also becomes greater, and therefore the memory is strained.
Further, in this magnetic head unit, since the amounts of deviation of the center of the read head core and the center of the write head core from the track change, the track position has been changed to measure the off-track margin to correct the amounts of deviation of the magnetic head cores. Therefore, to most improve the positioning precision in a write operation, at the time of writing, the read head core is positioned at the center of the target track for the write operation, while at the time of reading, the read head core is moved to the write position using the amount of deviation of the head core as the offset.
This deviation information is a value specific to the magnetic head unit, so is stored in a specific sector of the magnetic disk at the system used. In the related art, the read operation has been performed by searching for the specific sector by using the amount of correction of deviation of the design target or average of the manufacturing design and re-reading while changing the amount of offset until reading the specific sector.
Alternatively, the read operation has been performed by recording the amount of deviation specific to the magnetic head unit in a flash read only memory (ROM) or other nonvolatile memory, reading the deviation information from the nonvolatile memory at the time of turning the power on, and adding the amount of offset corresponding to the deviation for reading at the time of reading the specific sector. In recent years, however, the track density of the systems used has been increased, so the width of the write head core itself has become smaller and the amount of deviation with respect to the track width has become greater. Under this circumstance, if reading using the initial value based the design target or manufacturing average, a large number of offset read operations becomes necessary until finding the specific sector storing the amount of deviation specific to the magnetic head. In some cases, the phenomenon arises of normal reading becoming impossible.
Further, when recording the specific information in a nonvolatile memory, while the specific sector can be easily read at the time of turning on the power, a nonvolatile memory has to be mounted, so the cost rises. Further, in this case, not only is exchange of the printed circuit board on which the nonvolatile memory is mounted no longer easy, but also repair work at the time when a printed circuit board breaks down becomes no longer simple and a tremendous amount of time is required for the repair.
An object of the present invention is to provide a magnetic disk drive system designed to correct the read position or write position to prevent the problem unique to a magnetic head unit at the time of manufacture and simplifying the means for correcting position at the time of writing data to or reading data from a magnetic disk.
To achieve the above object, according to the present invention, there is provided a magnetic disk drive system wherein a magnetic head unit able to move over a rotating magnetic disk in the radial direction of the disk has a write head and a read head arranged in parallel separated by a certain distance and can write data on the magnetic disk or read data from the magnetic disk, provided with a write/read head distance measuring means for measuring distance information between the write head and said read head, a storage means for storing the measured write/read head distance information, and a control means for correcting an operation of the magnetic head unit based on the write/read head distance information read from the storage means.
Preferably, the write/read head distance information is stored in a specific sector at a predetermined track position on the magnetic disk or in a nonvolatile memory provided in the system.
Preferably, at a predetermined write start timing, the write/read head distance measuring means instructs the writing of measurement use write information in a sector selected for measurement by the write head at a first timing, then reads the write information by the read head, detects the predetermined positional information included in the write information, and produces a second timing and subtracts the time interval between the second timing and the write start timing from the time interval between the first timing and the second timing to measure the write/read head distance in the track direction for that magnetic head unit.
Further, preferably, when positioning the magnetic head unit on the measurement track, the write/read head distance measuring means shifts the magnetic head unit in the radial direction of the disk by exactly a predetermined amount of offset from the on-track position, reads the measurement information by the read head while subtracting a predetermined amount of offset from the offset position for every revolution of the magnetic disk, and measures the write/read head distance in the radial direction of the magnetic disk based on the amount of offset when the information can be read. It is also possible to measure the write/read head distance at a plurality of track positions on the magnetic disk and produce an n-ary polynomial for the write/read head distance for that track position based on the plurality of write/read head distance.
Further, the write/read head distance measuring means stores the order and coefficients in the n-ary polynomial in the storage means and, when reading by the read head, the control means finds the write/read head distance at the on-track position and adds an amount of offset based on the write/read head distance to the track position to perform a read seek operation.
Further, when writing specific information at a predetermined track position by the write head, the control means reads the write/read head distance information corresponding to that predetermined track position from the storage means, produces correction information based on the write/read head distance information, then sets the magnetic head unit on the predetermined track position, then writes the specific information by the write head at a position shifted from the predetermined track position by exactly the amount of the correction information.